U.S. patent number 6,442,855 [Application Number 09/790,657] was granted by the patent office on 2002-09-03 for tilt sensor.
This patent grant is currently assigned to Honda Giken Kogyo Kabushiki Kaisha. Invention is credited to Hiroshi Kawamoto, Yoshiaki Takeuchi.
United States Patent |
6,442,855 |
Takeuchi , et al. |
September 3, 2002 |
Tilt sensor
Abstract
A tilt angle sensor is disclosed that is capable of detecting
whether a tilt angle of a reference plane exceeds a predetermined
value by means of only one threshold value. Although only one
threshold value is used, the tilt angle can be measured with
respect to either a clockwise or a counterclockwise direction from
the untilted state. A pair of differential electrodes electrically
independent of each other are formed in a shape symmetric with
respect to upper and lower sections of a printed circuit board. A
common electrode plate is mounted opposed to the pair of
differential electrodes with a predetermined gap therebetween. The
pair of differential electrodes and the common electrode is stored
in a closed space formed by the printed circuit board and an oil
case. A dielectric liquid is filled into the closed space in such a
way that the level of the liquid varies according to the tilt of
the reference plane. An output signal corresponding to the
difference in capacity between two capacitors formed by associated
components is produced as a tilt detection output.
Inventors: |
Takeuchi; Yoshiaki (Saitama,
JP), Kawamoto; Hiroshi (Tochigi, JP) |
Assignee: |
Honda Giken Kogyo Kabushiki
Kaisha (Tokyo, JP)
|
Family
ID: |
18570629 |
Appl.
No.: |
09/790,657 |
Filed: |
February 23, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Feb 25, 2000 [JP] |
|
|
2000-048559 |
|
Current U.S.
Class: |
33/366.19;
33/366.11 |
Current CPC
Class: |
G01C
9/06 (20130101); G01C 9/20 (20130101); G01C
2009/062 (20130101); G01C 2009/185 (20130101) |
Current International
Class: |
G01C
9/06 (20060101); G01C 9/18 (20060101); G01C
9/00 (20060101); G01C 9/20 (20060101); G01C
009/06 () |
Field of
Search: |
;33/336.19,366.11,366.25
;340/689 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
453528 |
|
Dec 1992 |
|
JP |
|
514168 |
|
Apr 1993 |
|
JP |
|
Primary Examiner: Bennett; G. Bradley
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Claims
What is claimed is:
1. A tilt sensor comprising: a printed circuit board disposed in a
direction normal to a reference plane for measuring a tilt angle; a
pair of differential electrodes mounted on the printed circuit
board; a common electrode plate opposed to the pair of differential
electrodes with a predetermined gap formed between said
differential electrodes; a common electrode fixed to the printed
circuit board by a terminal formed from the common electrode plate;
a dielectric liquid filled into a closed space in a state where its
surface level varies according to the tilt angle of the reference
plane; a signal processing circuit section formed on the printed
circuit board, said signal processing circuit section producing an
output signal corresponding to a difference in capacity between two
capacitors, each capacitor includes the common electrode and a
respective differential electrode of said pair of differential
electrodes, as a tilt angle detection output, wherein the pair of
differential electrodes are mounted electrically independently of
each other in upper and lower regions respectively, wherein said
upper and lower regions are divided by a horizontal centerline,
said horizontal centerline passing through a center of gravity of
said printed circuit board in a direction normal to a direction of
gravity when said printed circuit board is in a no tilt condition,
and said pair of differential electrodes are formed in shapes
symmetrical to said horizontal centerline and a vertical centerline
of said printed circuit board, said vertical centerline passing
through said center of gravity and normal to said horizontal
centerline; and an oil case for storing the pair of differential
electrodes and the common electrode plate and forming said closed
space between itself and the printed circuit board.
2. The tilt sensor according to claim 1, wherein the dielectric
liquid is filled into the closed space to the level of the
horizontal centerline.
3. The tilt sensor according to claim 1, wherein the signal
processing circuit section further comprises: a buffer circuit for
receiving an exterior signal of a predetermined frequency and
supplying it to the common electrode; a first capacity-voltage
conversion circuit for rectifying a first capacitor signal taken
out of a first capacitor of said two capacitors and converting said
first capacitor signal into a first output voltage; a second
capacity-voltage conversion circuit for rectifying a second
capacitor signal taken out of a second capacitor of said two
capacitors and converting said second capacitor signal into a
second output voltage; and a differential amplifier circuit for
producing a differential voltage between the first output voltage
and the second output voltage.
4. The tilt sensor according to claim 1, wherein the dielectric
liquid is filled into the closed space to the level of the
horizontal centerline.
5. The tilt sensor according to claim 1, wherein said no tilt
condition of said printed circuit board occurs when said horizontal
centerline is normal with the direction of gravity and said tilt
angle is equal to zero degrees.
6. The tilt sensor according to claim 1, wherein said pair of
differential electrodes includes an upper differential electrode
and a lower differential electrode formed of copper foil
patterns.
7. The tilt sensor according to claim 6, wherein said upper and
lower differential electrodes are fan-shaped and have a
corresponding open angle S, wherein said open angle S is set
according to a desired range of tilt angle to be measured.
8. The tilt sensor according to claim 7, wherein a predetermined
threshold tilt angle value .theta.a for said tilt sensor defines
said open angle S according to the relationship of
S=(90-.theta.a).multidot.2.
9. The tilt sensor according to claim 1, wherein said common
electrode plate includes a pair of terminals corresponding to a
pair of terminal holes formed on said printed circuit board.
10. The tilt sensor according to claim 1, wherein said oil case is
bonded to said printed circuit board with bonding means.
11. The tilt sensor according to claim 2, wherein said differential
electrodes, said common electrode and said oil case are arranged
parallel to each other and vertically arranged so that a center of
gravity of said common electrode is aligned with a center of
gravity of said oil case.
12. The tilt sensor according to claim 1, wherein electrostatic
shielding plate is mounted on said printed circuit board and covers
said oil case and said signal processing section.
13. The tilt sensor according to claim 2, wherein said common
electrode plate includes through holes for permitting purging of
air and filling of dielectric liquid.
14. The tilt sensor according to claim 12 further comprising a
conductive plate fixedly engaged with an outer surface of said oil
case, wherein said conductive plate is secured to said printed
circuit board with conductive fixing pins through said oil
case.
15. The tilt sensor according to claim 3, wherein an output voltage
of said tilt sensor produced at an output terminal of said tilt
sensor is supplied to a control circuit.
16. The tilt sensor according to claim 15, wherein said control
circuit further comprises a microcomputer including a CPU; a system
bus, a program ROM for storing a predetermined threshold tilt value
detection program; a work area RAM; and I/O ports.
17. A tilt sensor comprising: a printed circuit board disposed in a
direction normal to a reference plane for measuring a tilt angle; a
pair of differential electrodes mounted on the printed circuit
board, said differential electrodes are electrically independent of
each other; a common electrode plate opposed to the pair of
differential electrodes with a predetermined gap therebetween; a
common electrode fixed to the printed circuit board by a terminal
formed from the common electrode plate; an oil case for storing the
pair of differential electrodes and the common electrode plate in a
closed space formed by said oil case and the printed circuit board;
a dielectric liquid filled into the closed space in a state where a
dielectric liquid surface level varies according to the tilt angle
of the reference plane; and a signal processing circuit section
which is formed on the printed circuit board and is capable of
producing the output signal of the level corresponding to the
difference in capacity between two capacitors, each of said two
capacitors includes the common electrode and an electrode from the
pair of the differential electrodes, as a tilt detection output,
wherein the pair of differential electrodes are mounted
electrically independently of each other in the regions which are
divided by a first intersection where a plane parallel to the
reference plane intersects the printed circuit board, and are
formed in a shape symmetric with respect to the first intersection
and each of the pair of differential electrodes is formed in a
shape symmetric with respect to a second intersection where a plane
normal to the reference plane intersects the printed circuit board;
wherein the dielectric liquid is filled into the closed space to
the level of the first intersection; and wherein the signal
processing circuit section comprises: a buffer circuit for
receiving a signal of a predetermined frequency from the outside
and supplying it to the common electrode; a first capacity-voltage
conversion circuit for rectifying a signal taken out of a first
capacitor constituted by the common electrode and one electrode of
the pair of differential electrodes and converting it into voltage;
a second capacity-voltage conversion circuit for rectifying a
signal taken out of a second capacitor constituted by the common
electrode and the other electrode of the pair of differential
electrodes and converting it into voltage; and a differential
amplifier circuit for producing a difference voltage output between
the output voltage of the first capacity-voltage conversion circuit
and that of the second capacity-voltage conversion circuit.
18. The tilt sensor according to claim 17, wherein said
differential electrodes, said common electrode and said oil case
are arranged parallel to each other and vertically arranged so that
a center of gravity of said common electrode is aligned with a
center of gravity of said oil case.
19. The tilt sensor according to claim 18, wherein said
differential electrodes are fan-shaped and have a corresponding
open angle S, wherein said open angle S is set according to a
desired range of tilt angle to be measured.
20. The tilt sensor according to claim 19, wherein a predetermined
threshold tilt angle value .theta.a for said tilt sensor defines
said open angle S according to the relationship of
S=(90-.theta.a).multidot.2.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatic type tilt sensor
which is used for detecting a tilt angle with respect to a plane
perpendicular to the direction of gravity, more particularly to a
tilt sensor providing an alarm or conducting a predetermined
control when a detected tilt angle exceeds a predetermined
value.
2. Background Art
Conventional tilt sensors employing a tilt detection element are
described in Japanese Unexamined Utility Model Publication No.
4-53528 and Japanese Examined Utility Model Publication No.
5-14168. An electrostatic type tilt sensor having these types of
conventional structure is shown in FIG. 5 and FIG. 6.
FIG. 5 is an exploded view of a conventional tilt sensor. FIG. 6 is
a cross-sectional view of a conventional tilt sensor along a plane
cut normal to a front surface of the tilt detection element.
A printed circuit board 1 made of a heat resistant material, for
example a laminate plate made of glass cloth and epoxy resin, is
disposed vertically with respect to a reference plane for measuring
a tilt angle when a tilt sensor is fixed to an object whose tilt
angle is to be measured. In FIG. 5, this reference plane is
designated by the plane including an imaginary line L0 represented
by a double-dotted and dashed line. This plane defined by the
imaginary line L0 becomes a reference plane from which to measure
tilt angle.
The reference plane is in a "0 degree" tilt angle when the
reference plane includes a line normal to the direction of gravity.
In the printed circuit board 1, a pair of differential electrodes
2a, 2b are formed of a copper foil pattern electrically independent
of each other in two regions. The two regions (left and right) are
defined by a plane formed along the intersection of (an imaginary
line L1 shown by a double dot and dash line in FIG. 5) both the
reference plane and the surface of the printed circuit board 1.
The signal processing circuit section of the tilt sensor, which
includes a printed wiring pattern and related electronic parts will
be described hereinafter. The signal processing circuit section is
mounted on a surface opposite to the surface on which the
differential electrodes 2a, 2b of the printed circuit board 1 are
formed. The respective differential electrodes 2a, 2b are connected
to the copper foil pattern on the surface of the printed circuit
board 1. The signal processing circuit section is formed via
through holes, at the electrode points 2c, 2d shown in FIG. 5.
The pair of differential electrodes 2a, 2b are formed as an
electrode pattern which is symmetric with respect to the imaginary
line L1. Also, each electrode of the pair of differential
electrodes 2a, 2b is formed as an electrode pattern which is
symmetric with respect to the imaginary line L2. Imaginary line L2
is the line that is normal to the imaginary L1 in FIG. 5. In the
example shown in FIG. 5, each of the differential electrodes 2a, 2b
is shaped like a horizontal fan.
In the example shown in FIG. 5, the arc-shaped periphery of each of
the differential electrodes 2a, 2b follows the shape a circular
arc. The circular arc is defined by a circle with its center at the
point of intersection of the imaginary line L1 and the imaginary
line L2. In this example, the diameter of the circle is set at 30
mm.
A reference numeral 3 designates a common electrode plate formed of
a conductive material having a desired rigidity. As shown in FIG.
6, this common electrode plate 3 is mounted on the printed circuit
board 1 in a state where it is held in parallel to the differential
electrodes 2a, 2b with a certain gap between them. A plurality of
terminals 3a, 3b, 3c, 3d are inserted into the printed circuit
board I which are integral with the common electrode plate 3 and
are formed by bending the plate 3 at right angles. The terminals
3a, 3b, 3c, 3d are inserted into terminal holes 4a, 4b, 4c, 4d made
in the printed circuit board 1 and are secured by soldering them to
the surface of the printed circuit board 1 on which the signal
processing circuit section is formed.
An oil case 5 formed of plastics having a desired flexibility is
formed in the shape of a letter U in cross section. When an end
face of the oil case 5 is bonded to the printed circuit board 21
with bonding means such as a double-faced adhesive tape 5B or the
like, the oil case 5 forms a closed space with the surface of the
printed circuit board 1.
The peripheries of the differential electrodes 2a, 2b, the
periphery of the common electrode 3, and the periphery of the case
5 are formed concentrically with each other. The opposite faces of
the differential electrodes 2a, 2b, that of the common electrode 3,
and the corresponding face of the case 5 are formed in parallel to
each other.
The closed space formed by the case 5 and the printed circuit board
1 is filled with a dielectric liquid 7 such as a silicone oil or
the like. The dielectric liquid 7 is poured from a through hole 6
made in the printed circuit board 1 to the level of approximately
half the effective volume in the closed space, e.g. to the level of
the imaginary line L2 shown in FIG. 5. The through hole 6 of the
printed circuit board 1 is filled with the dielectric liquid 7 and
is then sealed.
An electrostatic shielding plate 8 is mounted on a side of the
printed circuit board 1 to cover the case 5 and its surroundings
and the electrostatic shielding plate 9 is mounted on a second side
of the printed circuit board 1 to cover the signal processing
circuit section described hereinafter.
FIG. 7 is a schematic view of a signal processing circuit section
of an exemplary, conventional tilt sensor. In FIG. 7, an oscillator
11 and the output terminal thereof are connected to the common
electrode plate 3 of the tilt detection element 10 having the
characteristics described in FIG. 5 and FIG. 6. Further, the pair
of differential electrodes 2a, 2b of the tilt detection element 10
are connected to the input terminals of capacity-voltage conversion
circuits 12a, 12b, respectively.
The output terminals of the capacity-voltage conversion circuits
12a, 12b are connected to the input terminals of a differential
amplifier circuit 13, respectively. An output terminal 14 of the
tilt sensor is led out of the differential amplifier circuit 13.
The signal processing circuit section is provided with a power
stabilizing circuit 15 and the stabilized voltage supplied from
this power stabilizing circuit 15 is supplied to the oscillator 11
and the differential amplifier circuit 13 as a power supply
voltage.
Since the signal processing circuit section is arranged in the
manner described hereinabove, an oscillation output signal of a
predetermined frequency from the oscillator 11 is supplied to the
capacity-voltage conversion circuits 12a through a first capacitor
connected by the differential electrode 2a and the common electrode
plate 3 and also to the capacity-voltage conversion circuits 12b
through a second capacitor connected by the differential electrode
2b and the common electrode plate 3.
Accordingly, peak value signals corresponding to the capacity of
the first capacitor and the capacity of the second capacitor are
applied to the capacity-voltage conversion circuits 12a, 12b,
respectively.
The capacity-voltage conversion circuits 12a, 12b rectify the input
signals, and produce smoothed voltage. Therefore, the respective
output voltages of the capacity-voltage conversion circuits 12a,
12b correspond to peak values of the input signals. The capacity of
the first capacitor and the capacity of the second capacitor
correspond to their respective input signals.
Therefore, the differential amplifier circuit 13 produces a
differential voltage between the output voltage of the
capacity-voltage conversion circuits 12a and the output voltage of
the capacity-voltage conversion circuits 12b as the output of the
tilt sensor at the output terminal 14. In summary, the differential
amplifier circuit 13 produces an output voltage corresponding to
the difference in capacity between the first capacitor and the
second capacitor.
The tilt sensor, provided with the tilt detection element 10 and
the signal processing circuit section, is mounted on a plane to be
measured, e.g. the reference plane for measuring the tilt of the
object to be measured as described above. The tilt sensor is placed
such that the surface of the printed circuit board 1 of the tilt
detection element 10 becomes the plane to be measured.
When a plane to be measured is not tilted in the tilt direction
that is desired to be measured, a differential voltage of zero is
obtained. The plane to be measured includes a line normal to the
direction of gravity and essentially remains unchanged. Under this
condition, the dielectric liquid 7 is brought into a state where
approximately half of the respective differential electrodes 2a, 2b
are immersed dipped in the dielectric liquid 7. Accordingly, the
capacity of the first capacitor associated with the differential
electrode 2a and the common electrode plate 3 are equal to the
capacity of the second capacitor associated with the differential
electrode 2b and the common electrode plate 3. Therefore, the
difference in output voltage between the capacity-voltage
conversion circuits 12a, 12b becomes zero. The output voltage of
the differential amplifier circuit 13 becomes a corresponding
voltage Vo.
When the plane to be measured is tilted in the tilt direction to be
measured, the liquid levels of the dielectric liquid 7 will change.
The liquid level of the dielectric liquid 7 is brought into a state
where one of the differential electrodes 2a, 2b is immersed in the
dielectric liquid 7 in proportion to the tilt angle experienced by
the plane being measured (e.g., surface of the printed circuit
board 1) and the opposite differential electrode 2a, 2b is no
longer exposed to the dielectric liquid 7 in proportion to the tilt
angle experienced by the plane being measured. A difference in
capacity is produced by this effect corresponding to (and
representative of) the tilt angle between the first capacitor and
the second capacitor.
As seen in FIG. 5, when the plane to be measured is tilted in the
+.theta. direction (for example, counterclockwise) from the
position where the tilt angle is 0 degree, the capacity of the
first capacitor is decreased and the capacity of the second
capacitor is increased. Therefore, the output voltage of the
capacity-voltage conversion circuit 12a becomes larger than that of
the capacity-voltage conversion circuit 12b. Therefore, the output
voltage of the differential amplifier circuit 13 is made larger
than the voltage Vo by the amount corresponding to the tilt angle
in the +.theta. direction.
On the other hand, when the plane to be measured is tilted in the
-.theta. direction (for example, clockwise) from the position where
the tilt angle is 0 degree, the capacity of the second capacitor is
decreased and the capacity of the first capacitor is increased and
hence the output voltage of the capacity-voltage conversion circuit
12a becomes smaller than that of the capacity-voltage conversion
circuit 12b. Therefore, the output voltage of the differential
amplifier circuit 13 is made smaller than the voltage Vo by the
amount corresponding to the tilt angle in the -.theta.
direction.
The differential amplifier circuit 13 produces the voltage
corresponding to the difference in the output voltage between the
capacity-voltage conversion circuits 12a, 12b, or the difference in
capacity between the two capacitors.
FIG. 8 is a graphical view showing output voltage characteristics
of a conventional tilt sensor. As seen in FIG. 8, the output
voltage of the differential amplifier circuit 13 is a direct
current varying linearly in proportion to the tilt angle of the
plane to be measured from the position where the plane to be
measured at tilt angle=0, wherein the tilt angle includes the tilt
direction from the position where the plane to be measured at tilt
angle=0.
In aforementioned structure, the differential electrodes 2a, 2b and
the common electrode plate 3 are shaped like the fan described
above so that the output voltage of the differential amplifier
circuit 13 corresponds linearly to a change in the tilt angle, as
shown in FIG. 8.
The measurement of tilt angle through this type of conventional
tilt sensor is often used to provide an alarm indicating that the
plane to be measured is tilted more than a predetermined value. A
threshold voltage is set for the output voltage of the differential
amplifier circuit 13. An alarm is issued when the output voltage
exceeds the threshold voltage. Here, since the output voltage
characteristics of a conventional tilt sensor vary linearly with
respect to the tilt angle, threshold voltages are set for each tilt
angle direction, e.g. a threshold voltage V1 corresponding to a
threshold tilt angle for tilt angles in the +.theta. direction and
a threshold voltage V2 corresponding to a threshold tilt angle for
tilt angles in the -.theta. direction.
An alarm circuit includes a first detection circuit for issuing an
alarm when the output voltage of the differential amplifier circuit
13 is larger than the voltage V1 when the plane to be measured is
tilted in the +.theta. direction and at a second detection circuit
for issuing an alarm when the output voltage of the differential
amplifier circuit 13 is smaller than the voltage V2 when the plane
to be measured is tilted in the -.theta. direction.
However, in the aforementioned arrangements using a conventional
tilt sensor, the alarm circuit is necessarily complex. Since the
alarm circuit is required to set different threshold voltages and
to have different detection circuits for both tilt directions
(+.theta. and -.theta.) from the position where the plane to be
measured is at the tilt angle of 0 degrees.
SUMMARY OF THE INVENTION
The present invention overcomes the shortcomings associated with
the related art and achieves other advantages not realized by the
related art.
An aspect of the present invention is to provide a tilt sensor
capable of detecting variations in tilt angle for use in an alarm
circuit utilizing only one threshold value.
An aspect of the present invention is to provide an alarm circuit
having a tilt sensor that utilizes one threshold value for tilt
angle that is indicative of tilt angle, irrespective of the
direction of tilt of the plane to be measured from the 0 degree or
no-tilt position.
These and other aspects are accomplished by a tilt sensor
comprising a printed circuit board disposed in a direction normal
to a reference plane for measuring a tilt angle; a pair of
differential electrodes mounted on the printed circuit board; a
common electrode plate opposed to the pair of differential
electrodes with a predetermined gap formed between the differential
electrodes; a common electrode fixed to the printed circuit board
by a terminal formed from the common electrode plate; a dielectric
liquid filled into a closed space in a state where its surface
level varies according to the tilt angle of the reference plane; a
signal processing circuit section formed on the printed circuit
board, the signal processing circuit section producing an output
signal corresponding to a difference in capacity between two
capacitors, each capacitor includes the common electrode and a
respective differential electrode of the pair of differential
electrodes, as a tilt angle detection output, wherein the pair of
differential electrodes are mounted electrically independently of
each other in upper and lower regions respectively, wherein the
upper and lower regions are divided by a horizontal centerline, the
horizontal centerline passing through a center of gravity of the
printed circuit board in a direction normal to a direction of
gravity when the printed circuit board is in a "no tilt" condition,
and the pair of differential electrodes are formed in shapes
symmetrical to said horizontal centerline and a vertical centerline
of the printed circuit board, the vertical centerline passing
through said center of gravity and normal to the horizontal
centerline; and an oil case for storing the pair of differential
electrodes and the common electrode plate and forming the closed
space between itself and the printed circuit board.
These and other aspects are accomplished by a tilt sensor
comprising a printed circuit board disposed in a direction normal
to a reference plane for measuring a tilt; a pair of differential
electrodes mounted on the printed circuit board, which are
electrically independent of each other; a common electrode plate
opposed to the pair of differential electrodes with a predetermined
gap therebetween; a common electrode fixed to the printed circuit
board by a terminal formed of the common electrode plate; a case
body for storing the pair of differential electrodes and the common
electrode plate in the closed space formed by itself and the
printed circuit board; a dielectric liquid filled into the closed
space in the state where its surface level varies according to the
tilt of the reference plane; and a signal processing circuit
section which is formed on the printed circuit board and is capable
of producing the output signal of the level corresponding to the
difference in capacity between two capacitors, each of which is
constituted of the common electrode and each of the pair of the
differential electrodes, as a tilt detection output, wherein the
pair of differential electrodes are mounted electrically
independently of each other in the regions which are divided by a
first intersection where a plane parallel to the reference plane
intersects the printed circuit board, and are formed in a shape
symmetric with respect to the first intersection, and each of the
pair of differential electrodes is formed in a shape symmetric with
respect to a second intersection where a plane normal to the
reference plane intersects the printed circuit board; wherein the
dielectric liquid is filled into the closed space to the level of
the first intersection; and
wherein the signal processing circuit section includes: a buffer
circuit for receiving a signal of a predetermined frequency from
the outside and supplying it to the common electrode; a first
capacity-voltage conversion circuit for rectifying a signal taken
out of a first capacitor constituted by the common electrode and
one electrode of the pair of differential electrodes and converting
it into voltage; a second capacity-voltage conversion circuit for
rectifying a signal taken out of a second capacitor constituted by
the common electrode and the other electrode of the pair of
differential electrodes and converting it into voltage; and a
differential amplifier circuit for producing the difference between
the output voltage of the first capacity-voltage conversion circuit
and that of the second capacity-voltage conversion circuit.
When a tilt sensor according to the present invention is mounted on
a reference plane for measuring a tilt angle, e.g. the surface of
the printed circuit board 1 becomes a the plane to be measured, the
output signal of the signal processing circuit section has the
following varying characteristics.
In the zero degree, or "no tilt" condition, the plane to be
measured is not tilted in the tilt direction to be measured and
only one of the pair of differential electrodes is dipped in the
dielectric liquid and the output signal of the signal processing
circuit section becomes a predetermined value Vn. The predetermined
value Vn corresponds to the difference in capacity between the two
capacitors.
When the plane to be measured is tilted in either tilt direction to
be measured, the output signal of the signal processing circuit
section becomes approximately the predetermined value Vn described
above in the range of the tilt angle where the level of the
dielectric liquid does not reach the other electrode of the pair of
differential electrodes. Where the plane to be measured is tilted
in either the +.theta. or -.theta. tilt directions, as described
above, the predetermined value Vn is approximately obtained.
When the plane to be measured is further tilted in either tilt
direction, and the level of the dielectric liquid reaches the other
differential electrode of the pair of differential electrodes,
variations in capacity corresponding to either differential
electrode are obtained. In either of the cases where the plane to
be measured is tilted in the +.theta. or -.theta. directions, a
part of one differential electrode will be removed from the
dielectric liquid by some degree and a part of the other
differential electrode will become immersed in the dielectric
liquid by a corresponding amount.
In this state, the capacity of the capacitor which has been dipped
in the dielectric liquid is decreased (formed of one differential
electrode and the common electrode), while the capacity of the
capacitor which is dipped in the dielectric liquid is increased
(formed of the other differential electrode and the common
electrode).
Accordingly, the difference in capacity between the two capacitors
is decreased and hence the level of the output signal from the
signal processing circuit section is decreased relative to the tilt
angle. Here, the output signal varies in the same way in either of
the cases where the plane to be measured is tilted in the either
the +.theta. or -.theta. tilt direction, as described above.
Therefore, according to the present invention, the number of
threshold values required for detecting a tilt angle larger than a
predetermined tilt angle is reduced to one threshold value used for
either tilt direction.
Further scope of applicability of the present invention will become
apparent from the detailed description given hereinafter. However,
it should be understood that the detailed description and specific
examples, while indicating preferred embodiments of the invention,
are given by way of illustration only, since various changes and
modifications within the spirit and scope of the invention will
become apparent to those skilled in the art from this detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the
detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not intended to limit the present invention to the embodiments
shown, and wherein:
FIG. 1 is an exploded view of a tilt sensor according to an
embodiment of the present invention;
FIG. 2 is a cross-sectional view of a tilt sensor according to an
embodiment of the present invention;
FIG. 3 is a schematic view of a signal processing circuit section
of a tilt sensor according to an embodiment of the present
invention;
FIG. 4 is a graphical view showing output voltage characteristics
of a tilt sensor according to an embodiment of the present
invention;
FIG. 5 is an exploded view of a conventional tilt sensor;
FIG. 6 is a cross-sectional view of a conventional tilt sensor;
FIG. 7 is a schematic view of a signal processing circuit section
of an exemplary, conventional tilt sensor; and
FIG. 8 is a graphical view showing output voltage characteristics
of a conventional tilt sensor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, the present invention will be described in detail with
reference to the accompanying drawings. FIG. 1 is an exploded view
of a tilt sensor according to an embodiment of the present
invention. FIG. 2 is a cross-sectional view of the tilt detection
element of the tilt sensor taken along a plane cut normal to a
front plane FIG. 3 is a schematic view of a signal processing
circuit section of a tilt sensor according to an embodiment of the
present invention. FIG. 4 is a graphical view showing output
voltage characteristics of a tilt sensor according to an embodiment
of the present invention.
A printed circuit board 21 made of a heat resistant material, for
example, a laminate made of glass cloth and epoxy resin, is
disposed vertically with respect to a reference plane for measuring
a tilt angle when a tilt sensor is fixed to an object whose tilt
angle is to be measured. In FIG. 1, the reference plane is
designated by a plane including an imaginary line L0 shown by a
double-dotted and dashed line. This reference plane becomes a plane
to be measured. This plane defined by the imaginary line L0 becomes
a reference plane from which to measure tilt angle.
The reference plane is in a "0 degree" tilt angle when the
reference plane includes a line normal to the direction of gravity.
In the printed circuit board 21, a pair of differential electrodes
22a, 22b are formed of a copper foil pattern electrically
independent of each other in two regions. The two regions (upper
and lower) are defined by a plane formed along the intersection of
(an imaginary line L2 shown by a double-dotted and dashed-line in
FIG. 5) both the reference plane and the surface of the printed
circuit board 21.
The signal processing circuit section of the tilt sensor, which
includes a printed wiring pattern and associated electronic parts
will be described hereinafter. The signal processing circuit
section is mounted on the surface opposite to the surface on which
the differential electrodes 22a, 22b of the printed circuit board
21 are formed. The respective differential electrodes 22a, 22b are
connected to the copper foil pattern on the surface of the printed
circuit board 21 where the signal processing circuit section is
formed via through holes, at the electrodes points 22c, 22d shown
in FIG. 1.
The pair of differential electrodes 22a, 22b are formed as an
electrode pattern of a shape symmetric with respect to the
imaginary line L2. Also, each of the pair of differential
electrodes 22a, 22b is formed as an electrode pattern of a shape
which is symmetric with respect to the imaginary line L1. The
imaginary line L1 is normal to the imaginary L2 and/or the
reference plane. In the example shown in FIG. 1, each of the
differential electrodes 22a, 22b is shaped like a vertical fan.
In the example shown in FIG. 1, the arc-shaped periphery of each of
the differential electrodes 22a, 22b is a circular arc which
follows the path of a circle with its center at the point of
intersection of the imaginary line L1 and the imaginary line L2. In
this preferred embodiment, the diameter of the circle is set at 14
mm, for example.
In this case, the open angle S of each of the fan-shaped
differential electrodes 22a, 22b is set according to the desired
range of measured tilt angle. This range is set based upon the
required output signal of the tilt sensor necessary to provide a
linear characteristic to a change in tilt. When the output
characteristic of the tilt sensor is required to be linear in the
range where the tilt angle from the position where the tilt angle
is 0 degree is larger than a predetermined value .theta.a, the open
angle S is defined as S=(90-.theta.a).multidot.2. In this example,
the open angle S is set at 100 degrees for the purpose of making
the output characteristic larger than 40 degrees from the tilt
angle from the 0 degree position.
A reference numeral 23 designates a common electrode plate formed
of a conductive material having a desired rigidity. This common
electrode plate 23 is shaped like a gourd such that the common
electrode 23 exactly matches the pair of differential electrodes
22a, 22b when it is placed thereon.
In this embodiment, the common electrode plate 23 is mounted on the
printed circuit board 21 in a state where it is held in parallel to
the differential electrodes 22a, 22b with a gap between them. As
shown in FIG. 2, the common electrode plate 23 is mounted by
inserting two terminals 23a, 23b, which are integral with the plate
23 and formed by bending the plate 23 at right angles, into the
terminal holes 24a, 24b made in the printed circuit board 21. The
terminals 23a, 23b are then soldered to the surface of the printed
circuit board 21 on which the signal processing circuit section is
formed.
As shown in FIG. 1, the two terminals 23a, 23b formed of the common
electrode plate 23 are formed on the constricted portion of the
gourd-like shape of the common electrode plate 23 and are inserted
into the terminal holes 24a, 24b made between the differential
electrodes 22a, 22b in the portion of the printed circuit board 21
where the electrode pattern is not formed. This can reduce the tilt
detection element size in at least one direction (e.g. the
horizontal direction in FIG. 1).
An oil case 25 formed of plastics having proper flexibility is
shaped like a letter U in cross section. As shown in FIG. 2, the
oil case 25 forms a closed space with the printed circuit board 21
when its end face is bonded to the printed circuit board 21 with
bonding means such as a double-faced adhesive tape 25B or a similar
adhesive.
The differential electrodes 22a, 22b, the common electrode 23, and
the case 25 are arranged so that their opposite faces are parallel
to each other and that the center of gravity of the common
electrode 23 agrees with that of the case 25.
The closed space formed by the case 25 and the printed circuit
board 21 is filled with a dielectric liquid 27 such as a silicone
oil or the like. The dielectric liquid 27 is poured from a through
hole 26a made in the differential electrode 22a of the printed
circuit board 21 to a level of approximately half of the effective
volume in the closed space. This level of the imaginary line L2
defines this level as shown in FIG. 1.
The through hole 26a made in the differential electrode 22a of the
printed circuit board 21 is filled and sealed with solder from the
side of the printed circuit board 21 on which the signal processing
circuit section is mounted. After the closed space is filled with
the dielectric liquid 27, the through hole 26a is easily filled
with the solder because it is made in the copper foil pattern.
The linear characteristic portion of the output of the tilt sensor
described below is compensated by a differential electrode 22a
pairing with the differential electrode 22b. A through hole 26b is
filled and sealed with solder in the like manner described above.
In this case, the through hole 26a and the through hole 26b have
the same diameter and are made at positions symmetric with respect
to the imaginary line L2.
The height of the closed space from the printed circuit board 21 is
low, for example, 3 mm, and the distance between the printed
circuit board 21 and the common electrode plate 23, is only about
1.5 mm. The dielectric liquid 27 is injected into the closed space
with a nozzle like an injection needle inserted thereto. However
the distance between the printed circuit board 21 and the common
electrode plate, for example 1.5 mm, is too small to insert an
injection needle.
Therefore, in a preferred embodiment and as shown in FIG. 1,
through holes 23c, 23d having the same diameter are made in the
common electrode plate 23 at positions corresponding to the through
holes 26a, 26b of the differential electrodes 22a, 22b to ensure an
adequate distance to insert the nozzle for injecting the dielectric
liquid 27, for example 3 mm.
Since the through holes 23c, 23d of the common electrode plate 23
are symmetric with respect to the imaginary line L2, it is possible
to compensate the linear characteristic portion of the output of
the tilt sensor described below.
Further, one of the through holes at which the electrode points
22c, 22d are formed, e.g. the electrode point 22c in the embodiment
shown in FIG. 1, is used as a hole for purging air when the
dielectric liquid 27 is injected thereto. In order to compensate
the linear characteristic portion of the output of the tilt sensor,
the through hole at which the electrode points 22c, 22d are formed
are made in the differential electrodes 22a, 22b at the points
symmetric with respect to the imaginary line L2. The electrode
points 22c, 22d are sealed with solder after the dielectric liquid
27 is injected.
Electrostatic shielding plate 28, 29 for preventing the effect of
the outside is mounted on the printed circuit board 21 to cover the
case 25 and its surroundings. The electrostatic shielding plate 29
is mounted on the printed circuit board 21 to cover the signal
processing circuit section described below.
Also, a conductive plate 31 is fixed to the outer flat surface of
the oil case 25. This conductive plate 31 is fixed to the printed
circuit board 21 with conductive fixing pins 32 through the oil
case 25. The tip ends of the conductive fixing pins 32 are
connected to the grounded conductor of the printed circuit board
21. This arrangement ensures that the conductive plate 31 is
electrically grounded.
The portion of the printed circuit board 21, which the end face of
the oil case 25 is put into contact with and the double-faced
adhesive type 25B is placed on, is provided with the copper foil
pattern. The copper foil pattern is formed in a shape corresponding
to the end face of the oil case 25 for the purpose of making the
surfaces flat. This copper foil pattern is connected to an earth
pattern on the reverse surface side of the printed circuit board 21
via the hole through which the pin 32 is inserted to be
grounded.
FIG. 3 is a schematic view of a signal processing circuit section
of a tilt sensor according to an embodiment of the present
invention. In a preferred embodiment, a clock signal SC is enters
the signal processing circuit section through an input terminal 41.
In FIG. 3, this clock signal SC is supplied from a control circuit
50 mounted on a control circuit board other than the tilt
sensor.
The clock signal SC entered through the input terminal 41 and
having a predetermined frequency is wave-shaped by a clock buffer
42. The clock buffer 42 can be for example, a C-MOS (complementary
metal oxide semiconductor) inverter to correct the waveform of the
entered input clock signal.
The output terminal of this clock buffer 42 is connected to the
common electrode plate 23 of the tilt detection element 40 in the
preferred embodiment shown in FIG. 1 and FIG. 2, as described
above. The pair of differential electrodes 22a, 22b of the tilt
detection element 40 are connected to the input terminals of
capacity-voltage conversion circuits 43a, 43b, respectively.
The output terminals of the capacity-voltage conversion circuits
43a, 43b are connected to the input terminals of a differential
amplifier circuit 44. The output terminal 45 of the tilt sensor is
taken out of differential amplifier circuit 44.
Although omitted in FIG. 3, this signal processing circuit section
is not provided with a conventional power stabilizing circuit as
shown in FIG. 7, but is instead supplied with a stabilized power
supply voltage from an outside source.
Since the signal processing circuit section of this preferred
embodiment is arranged in this manner, the clock signal SC entered
through the input terminal 41 is wave-shaped by the clock inverter
42 and then is supplied to the capacity-voltage conversion circuits
43a,43b through first and second capacitors. The wave-shaped clock
signal SC is supplied to the capacity-voltage conversion circuit
43a, through the first capacitor which includes the differential
electrode 22a and the common electrode plate 23. The wave-shaped
clock signal SC is also supplied to the capacity-voltage conversion
circuits 43b through a second capacitor constituted by the
differential electrode 22b and the common electrode plate 23.
Here, peak value signals corresponding to the capacity Ca of the
first capacitor and the capacity Cb of the second capacitor are
supplied to the capacity-voltage conversion circuits 43a, 43b,
respectively. The capacity-voltage conversion circuits 43a, 43b
rectify the input signals, respectively, and produce smoothed
voltage.
The respective output voltages of the capacity-voltage conversion
circuits 43a, 43b have magnitudes corresponding to peak values of
the capacity-voltage conversion circuits 43a, 43b. The capacity Ca
of the first capacitor and the capacity Cb of the second capacitor
are these peak values.
Therefore, the differential amplifier circuit 44 produces the
differential voltage between the output voltage of the
capacity-voltage conversion circuits 43a and the output voltage of
the capacity-voltage conversion circuits 43b as the output of the
tilt sensor at the output terminal 45.
The output voltage of the tilt sensor produced at the output
terminal 45 is supplied to the control circuit 50. In this
embodiment, the control circuit 50 includes a microcomputer in
which a CPU 51, a system bus 52, a program ROM 53, a work area RAM
54, and I/O ports 55, 56, 57 is provided.
The control circuit 50 supplies the clock signal SC to the input
terminal 41 of the tilt sensor through the I/O port 56. An output
voltage from the output terminal 45 of the tilt sensor is applied
to the I/O port 55 of the control circuit 50 as a tilt detection
output through an A/D converter not shown.
The control circuit 50 detects, according to a tilt threshold value
detection program stored in the program ROM 52, whether the output
voltage of the tilt sensor exceeds a predetermined threshold
voltage or not. When the control circuit 50 detects that the output
voltage exceeds the threshold voltage, the control circuit 50
supplies a corresponding control signal to a section 60 to be
controlled to put a predetermined control into practice.
The tilt sensor provided with the tilt detection element 40 and the
signal processing circuit section is mounted on the plane to be
measured which is the reference plane for measuring tilt. As
described above, the input terminal 41 and the output terminal 45
are connected to the control circuit 50. The tilt sensor is placed
such that the surface of the printed circuit board 21 of the tilt
detection element 40 becomes the plane, including the tilt
direction, to be measured, as is the case described above.
When the plane to be measured is at the position where it is not
actually tilted, e.g the tilt angle is 0 degree (the plane to be
measured is a plane including a line normal to the direction of the
gravity), the entire differential electrode 22b is dipped in the
dielectric liquid 27. In contrast, the differential electrode 22a
is not exposed at all or remains undipped in the dielectric liquid
27.
Therefore, the capacity Cb of the second capacitor constituted by
the differential electrode 22b and the common electrode plate 23,
as a variable capacity corresponding to the amount of immersion in
the dielectric liquid, becomes a maximum. On the other hand, the
capacity Ca of the first capacitor constituted by the differential
electrode 22a and the common electrode plate 23 becomes a minimum
value.
FIG. 4 is a graphical view showing output voltage characteristics
of a tilt sensor according to an embodiment of the present
invention. The difference between the output voltages of the
capacity-voltage conversion circuits 43a, 43b becomes a maximum and
the output voltage of the tilt sensor exhibits a maximum value Vm
as shown in FIG. 4.
Even when the plane to be measured is tilted in the tilt direction
to be measured, as described above, in the range of tilt angle not
exceeding 40 degrees in this embodiment, the differential electrode
22a keeps the state in which the nearly all of the differential
electrode 22a is dipped in the dielectric liquid 27. That is, the
range of tilt angle which does not exceed the angle K=90-S/2
corresponding to the open angle S of fan-shaped differential
electrodes 22a, 22b, with respect to the reference plane.
Similarly, the differential electrode 22b maintains a state in
which the differential electrode 22a is hardly dipped in the
dielectric liquid 27.
Accordingly, the capacity Ca of the first capacitor and the
capacity Cb of the second capacitor are hardly varied and the
resulting output voltage of the differential amplifier 44 is kept
approximately at the voltage Vm.
When the plane to be measured is further tilted in the tilt
direction to be measured and the tilt angle exceeds the
above-mentioned K, in either of the cases where the direction of
tilt is in the direction of +.theta. or -.theta., a part of the
differential electrode 22a which has been nearly wholly dipped in
the dielectric liquid 27 is removed from the surface of the
dielectric liquid 27 and a part of the differential electrode 22b
is immersed by the same proportion into the dielectric liquid
27.
For this reason, the capacity Ca of the first capacitor formed of
the differential electrode 22a and the common electrode 23 is
increased and the capacity Cb of the first capacitor formed of the
differential electrode 22b and the common electrode 23 is
decreased.
Accordingly, the difference between the output voltage of the
capacity-voltage conversion circuit 43a and the output voltage of
the capacity-voltage conversion circuit 43b is reduced. Then, the
output voltage of the tilt sensor is decreased linearly in
accordance with an increase in the tilt angle in either of the
cases where the direction of tilt is in the +.theta. or -.theta.
directions.
Therefore, if the control circuit 50 previously determines a single
voltage Vth corresponding to a threshold tilt angle th detection
and detects whether the output voltage of the tilt sensor is
smaller than the voltage Vth, it is possible to detect whether the
plane to be measured is tilted more than the threshold tilt angle
th. This can be accomplished in either of the cases where the
direction of tilt is in the direction of +.theta. or -.theta..
In this case, the control circuit 50 can detect whether the plane
to be measured is tilted more than the threshold tilt angle th or
not by means of a software program for monitoring whether the
output voltage of the tilt sensor exceeds the single voltage Vth.
Therefore, this produces an advantage that monitoring is made by a
simple software, as compared with the conventional case where two
threshold voltages are monitored.
The control circuit 50 may comprise discrete hardwares instead of
the microcomputer. In this case, only a circuit for detecting
whether the output voltage of the tilt sensor exceeds the single
threshold voltage Vth is required. Therefore, it is not required to
arrange two detection circuits for detecting whether the tilt angle
exceeds separate threshold values in the direction of +.theta. or
-.theta. directions, respectively.
Also, in the case of the above preferred embodiment, the signal
processing circuit is not provided with an oscillator as is the
case with the conventional tilt sensor and the clock signal is
supplied from an external source. This arrangement can further
reduce the size of the tilt sensor of the present invention,
including the printed circuit board. Also, eliminating the
conventional power stabilizing circuit contributes to reducing the
size of the tilt sensor.
The output voltage of the capacity-voltage conversion circuit 43a
is supplied to the non-inversion input terminal of the differential
amplifier circuit 44 and the output voltage of the capacity-voltage
conversion circuit 43b is supplied to the inversion input terminal
of the differential amplifier circuit 44. Therefore, the
differential amplifier circuit 44 has the characteristics of the
output voltage shown in FIG. 4.
However, if applying the output voltages of the capacity-voltage
conversion circuits 43a, 43b to the input terminals of the
differential amplifier circuit 44 is the reverse of the case shown
in FIG. 3, the characteristics of the output voltage of the
differential amplifier circuit 44 is the reverse of those in the
case shown in FIG. 4.
That is, in the reverse case, when the difference between the
capacitance Ca of the first capacitor and the capacitance Cb of the
second capacitor is a maximum, the output voltage is a minimum. As
the difference between the two capacitances (Ca, Cb) decreases, the
output voltage increases. In this case, it is possible to detect
whether the plane to be measured is tilted more than the threshold
tilt angle th when detecting that the output voltage is larger than
the threshold voltage Vth.
The output signal varies in the same way in either of the cases
where the plane to be measured is tilted in the either the +.theta.
or -.theta. tilt direction, as described above. Therefore,
according to the present invention, the number of threshold values
required for detecting a tilt angle larger than a predetermined
tilt angle is reduced to one threshold value used for either tilt
direction.
The invention being thus described, it will be obvious that the
same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the are intended to be included within the scope of the following
claims.
* * * * *